The present invention relates to an on-vehicle actuator system having a motor driven by a 3-phase current.
As electronic and control technologies advance rapidly in recent years, a by-wire technology has been developed that can control an output mechanism on a vehicle side independently of an input mechanism on a driver's side during operations that determine vehicle actions such as driving, braking and steering. Since it can electronically control a relation between the driver's operations and vehicle movements, the by-wire technology can improve a feel and an operability when the driver drives a vehicle, thereby reducing fatigue of the driver. Independently of an intention of the driver, the by-wire technology can automatically apply brakes, run the vehicle at a constant speed, keep a constant distance from another car running in front and make the vehicle run along a traffic lane. It can also control an output of conventional output mechanisms to cooperate with a regeneration function not available conventionally.
Most of actuators based on the by-wire technology comprise a high-torque, high-speed motor. Car-mounted actuator systems using a motor that have been developed so far include a pedal device that generates a reactive force by a motor, a motor-driven brake that generates a thrust to press a frictional material against a brake rotor, and a motor-driven booster that generates a hydraulic pressure in a master cylinder according to a degree the driver steps on the brake. For example, JP-A-2006-281992 discloses an electric booster that can precisely estimate an input thrust to an input member by using a displacement sensor and, based on the estimated input thrust, drive the motor-driven actuator to improve a pedal feel by incorporating a jump-in characteristic when a brake pedal is slightly stepped on and to appropriately perform a brake assist control when a large input is applied to a brake pedal.